Wireless power transmission systems have been developed that wirelessly transmit power using electromagnetic induction, magnetic coupling, or the like. Examples of such a wireless power transmission system include systems for charging portable terminal devices.
Japanese Unexamined Patent Publication No. 2010-51137 discloses a transmitter and a receiver that perform non-contact power transmission using a magnetic resonance phenomenon. The receiver includes a received power detection circuit and a data transmission circuit that transmits a value measured by the received power detection circuit to the transmitter. The transmitter includes a data receiving circuit that receives the received power value data measured by the received power detection circuit, a transmitted power detection circuit that measures transmitted power, a transmitted power-received power comparison circuit that compares the received power value outputted by the data receiving circuit with the transmitted power value measured by the transmitted power detection circuit, a power control circuit that controls power to be transmitted on the basis of the comparison made by the transmitted power-received power comparison circuit, a storage unit that stores at least two power-to-be-transmitted setting values, and a warning LED that gives a warning to the user on the basis of the comparison made by the transmitted power-received power comparison circuit.
Japanese Unexamined Patent Publication No. 2009-278331 describes an example of a two-dimensional communication system that uses a two-dimensional communication sheet to allow power transmission between a communication apparatus and a terminal apparatus. When the amount of power stored in the terminal apparatus falls below a predetermined level in the two-dimensional communication system, the terminal apparatus sends a power transmission request message to the communication apparatus via the two-dimensional communication sheet. In response to the message, the communication apparatus transmits power via the two-dimensional communication sheet. The terminal apparatus receives the power from the communication apparatus and stores it. When the amount of the stored power reaches a predetermined level, the terminal apparatus sends a power transmission stop request message to the communication apparatus via the two-dimensional communication sheet. The communication apparatus stops transmitting power.